In Neurospora crassa, we have found that five proteins are covalently labelled with 14C pantothenate. The two most abundantly labelled proteins are found in the mitochondria. We propose to follow up on these observations in three principal ways: 1) to study the structure and identity of the pantothenate-labelled mitochondrial proteins; 2) to study the possible function for this post-translational modification of these proteins; and 3) to study the identity of the non-mitochondrial pantothenate-labelled proteins. The structural studies can be subdivided as follows: a) identifying the peptides that pantothenate is attached to; b) confirming that the ATPase and cytochrome oxidase complexes have a pantothenate-labelled subunit in them; and c) determining the site of synthesis, cytoplasmic vs. mitochondrial, of these subunits; The second aspect is to study the function of the pantothenate moiety as follows: a) analyses of certain mutants for possible defects in their pantothenate labelling profiles; b) analyses of possible functions for the pantothenate, such as attachment sites for fatty acids or thiols; and c) the determination of the pantothenate labelling pattern in other cells, particularly yeast and somatic cells. The third aspect of this proposal is an attempt to analyze the location of the two minor pantothenate-labelled proteins with respect to other membrane fractions in Neurospora. The proposed studies should yield some insight into whether the pantothenate moiety plays a general or specific role when attached to proteins and potentially could also yield some information about the role of particular subunits in the ATPase and cytochrome oxidase complexes of the mitochondria.